New to KubeDB? Please start here.

ClickHouse Volume Expansion

This guide will give an overview on how KubeDB Ops-manager operator expand the volume of various component of ClickHouse.

Before You Begin

• You should be familiar with the following KubeDB concepts:
  • ClickHouse
  • ClickHouseOpsRequest

How Volume Expansion Process Works

The following diagram shows how KubeDB Ops-manager operator expand the volumes of ClickHouse database components. Open the image in a new tab to see the enlarged version.

  

The Volume Expansion process consists of the following steps:

1. At first, a user creates a ClickHouse Custom Resource (CR).

2. KubeDB Provisioner operator watches the ClickHouse CR.

3. When the operator finds a ClickHouse CR, it creates required number of PetSets and related necessary stuff like secrets, services, etc.

4. Each PetSet creates a Persistent Volume according to the Volume Claim Template provided in the petset configuration. This Persistent Volume will be expanded by the KubeDB Ops-manager operator.

5. Then, in order to expand the volume of the various components (ie. Combined, Broker, Controller) of the ClickHouse, the user creates a ClickHouseOpsRequest CR with desired information.

6. KubeDB Ops-manager operator watches the ClickHouseOpsRequest CR.

7. When it finds a ClickHouseOpsRequest CR, it halts the ClickHouse object which is referred from the ClickHouseOpsRequest. So, the KubeDB Provisioner operator doesn’t perform any operations on the ClickHouse object during the volume expansion process.

8. Then the KubeDB Ops-manager operator will expand the persistent volume to reach the expected size defined in the ClickHouseOpsRequest CR.

9. After the successful Volume Expansion of the related PetSet Pods, the KubeDB Ops-manager operator updates the new volume size in the ClickHouse object to reflect the updated state.

10. After the successful Volume Expansion of the ClickHouse components, the KubeDB Ops-manager operator resumes the ClickHouse object so that the KubeDB Provisioner operator resumes its usual operations.

In the next docs, we are going to show a step-by-step guide on Volume Expansion of various ClickHouse database components using ClickHouseOpsRequest CRD.